Estimation and pre-compensation of harmonic coupling spurs

ABSTRACT

Examples of this description provide for a method. In some examples, the method includes determining, via a circuit, an estimated value of harmonic coupling in a transmitted signal via a feedback signal path that receives the transmitted signal and performing pre-compensation for the harmonic coupling based on the estimated value, the pre-compensation performed in the circuit.

BACKGROUND

Multiple input multiple output (MIMO) architectures (such as a fifthgeneration (5G) base station or dual band macro base station) includemultiple transmit antennas and multiple receive antennas to facilitateincreased throughput, such as via beamforming and spatial multiplexing.An increase in the number of antennas in a MIMO architecture candecrease physical spacing between the antennas.

SUMMARY

In some examples, a circuit has an input operable to receive data and anoutput operable to provide a transmitted signal. The circuit includes atransmission signal chain including a harmonic coupling cancellationcircuit operable to output a harmonic coupling cancellation signal, adigital up-conversion (DUC) circuit having an output, a first inputoperable to receive the harmonic coupling cancellation signal, and asecond input coupled to the circuit input, the DUC circuit operable tomodify the data by the harmonic coupling cancellation signal, and adigital-to-analog converter (DAC) having an input coupled to the outputof the DUC and having an output, the DAC configured to provide thetransmitted signal at the output of the DAC. The circuit also includes afeedback signal chain including an estimation circuit, the estimationcircuit operable to estimate a spurious harmonic coupling signalaccording to the transmitted signal, and provide values representativeof the estimate of the spurious harmonic coupling signal to the harmoniccoupling cancellation circuit. The harmonic coupling cancellation signalis based on the estimate of the spurious harmonic coupling signal.

In some examples, a system includes an amplifier having an input and anoutput and a transceiver. The transceiver has a communication interface,a transmit signal chain having an input coupled to an output of thecommunication interface and an output coupled to the input of theamplifier, wherein the transmit signal path is configured to provide asignal for transmission to the amplifier, and a feedback signal chainhaving an input coupled to the output of the amplifier and an outputcoupled to an input of the communication interface. The feedback signalchain is configured to estimate a spurious harmonic coupling componentof a signal transmitted by the amplifier, and provide valuesrepresentative of the estimate of the spurious harmonic couplingcomponent to the transmit signal path for compensation for the spuriousharmonic coupling component in the signal for transmission.

In some examples, a method includes determining, via a circuit, anestimated value of harmonic coupling in a transmitted signal via afeedback signal path that receives the transmitted signal and performingpre-compensation for the harmonic coupling based on the estimated value,the pre-compensation performed in the circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system, in accordance withvarious examples.

FIG. 2 is a block diagram of a transceiver, in accordance with variousexamples.

FIG. 3 is a block diagram of a transceiver, in accordance with variousexamples.

FIG. 4 is a flow diagram of a method of operation of a transceiver, inaccordance with various examples.

DETAILED DESCRIPTION

As physical spacing between antennas decreases, such as in a MIMOarchitecture in which an increased number of antennas are included(e.g., such as 32, 64, or more transmit (TX) antennas and 32, 64, ormore receive (RX) antennas), coupling (e.g., cross-talk and/orinterference) between transmit signal chains (which are connected tothose antennas) may occur. In some examples, the coupling iselectro-magnetic coupling. In other examples, the coupling may besubstrate coupling. The coupling may increase noise experienced bysignals being communicated via the transmit channel and/or reducing orotherwise degrading performance of a system that receives signalstransmitted via the transmit signal chains.

Some of the example embodiments may compensate for spurious signals in asignal chain of a device, such as may result from harmonic couplingbetween signal chains or components in an electronic device, to mitigateeffects of the coupling. For example, the compensation may improveisolation between or among the signal chains or components. In anexample, the compensation may be performed as a pre-compensation byproviding a frequency spur with a programmed amplitude, frequency, andphase in a digital baseband of the system. In some examples, theamplitude, frequency, and phase are determined by an estimationperformed during a power-up calibration of the system. The estimationmay be performed via a loopback from a transmitter output to anauxiliary receiver input, such as of a feedback path. For example, aprogrammed calibration signal (e.g., a signal having known or controlledvalues) may be provided to perform the estimation via the feedback path.During steady-state operation of the system, the amplitude and the phasemay be monitored and modified based on time and temperature variations.In at least some examples, the estimation is based on a measurementperformed based on a transmitted signal received at a feedback signalpath without the implementation of a dedicated time slot in transmissionfor measurement and estimation.

FIG. 1 is a block diagram of a communication system 100, in accordancewith various examples. In some examples, the communication system 100is, or includes, a MIMO architecture. For example, the communicationsystem 100 may be, or be a part of, a 5G base station or dual band macrobase station that facilitates communication according to a MIMOarchitecture or MIMO technologies. In some examples, the system 100includes a transceiver 102, an amplifier 104 (e.g., a power amplifier(PA)), a diplexer 106, an antenna 108, and an amplifier 110 (e.g., alow-noise amplifier (LNA)). The transceiver 102 may have an output(e.g., of a transmit signal path) coupled to an input of the amplifier104. The diplexer 106 has an input coupled to an output of the amplifier104. The transceiver 102 has a first input (e.g., a feedback signalpath) coupled to the output of the amplifier 104. The diplexer 106 has afirst input/output coupled to the antenna 108. The diplexer 106 has asecond output coupled to an input of the amplifier 110. The amplifier110 has an output coupled to a second input (e.g., a receive signalpath) of the transceiver 102.

In some examples, the transceiver 102 includes a digital interface 112(which may include, for example, a processor, memory, digital circuitry,analog circuitry and/or software), such as a serializer/deserializer(SerDes) interface and/or a JESD digital interface. The transceiver 102also includes a digital processing circuit 114 (which may include, forexample, a processor, memory, digital circuitry, analog circuitry and/orsoftware), a digital-to-analog converter (DAC) 116, a digital stepattenuator (DSA) 118, a DSA 120, an analog-to-digital converter (ADC)122, a digital processing circuit 124 (which may include, for example, aprocessor, memory, digital circuitry, analog circuitry and/or software),a DSA 126, an ADC 128, a digital processing circuit 130 (which mayinclude, for example, a processor, memory, digital circuitry, analogcircuitry and/or software), a reference clock (Fref) generation circuit132, and a phase-locked loop (PLL) circuit 134 (e.g., a digital PLL oran analog PLL).

The circuit 114 is coupled to, and configured to receive data from theinterface 112, and provide data to the DAC 116. In some examples, thecircuit 114 processes, modifies, alters, or otherwise interacts with thedata received from the interface 112 to create a signal that includesthe data and is pre-compensated for estimated harmonic coupling, such asestimated according to the teachings of the present disclosure. In anexample, the circuit 114 receives the signal which carries the data tobe transmitted and processes, modifies, alters, or otherwise interactswith the data and the signal by adding another signal to the receivedsignal. The other signal may be a compensation signal, as determinedaccording to the teachings of the present disclosure, for compensatingfor the spurious harmonic coupling described herein. In variousexamples, the circuit 114 may include various sub-circuits (not shown)such as interpolation filters, digital up conversion mixers, etc. tofacilitate further processing, modification, alteration, or interactionby the circuit 114, including interpolation and/or frequency translationto provide a signal for transmission.

The transmittable signal is provided to the DAC 116 for conversion froma digital signal to an equivalent analog signal. The DAC 116 is coupledand configured to provide the analog signal (that includes the datareceived from interface 112) to the DSA 118. DSA 118 selectivelyattenuates all or a portion of the analog signal. Power amplifier 104amplifies the attenuated analog signal so that the amplified signal maybe transmitted via switch/diplexer 106 and antenna 108. In someimplementations, the circuit 114, the DAC 116, and the DSA 118 form, orare components of, a transmit signal path of the transceiver 102. Insome examples, harmonic coupling (e.g., such as electro-magnetic orsubstrate coupling) may occur between the DSA 118 and the amplifier 104.For example, harmonics of a Fref of the transceiver may undesirablycouple to an output of the DSA 118, adversely affecting operation of thetransceiver 102. In addition, as is shown in FIG. 1 , harmonic couplingmay be present from Fref circuitry 132 at the output of DSA 118. The DSA120 is coupled and configured to receive data from the amplifier 104 andprovide data to the ADC 122. The DSA 120 selectively attenuates (e.g.,attenuates certain frequencies or frequency bands more or less thanother frequencies or frequency bands) the amplified analog signal (e.g.,the output of PA 104) to protect the circuitry in the feedback path(namely, ADC 122 and digital circuitry 124). The ADC 122 is coupled andconfigured to convert the attenuated analog signal to an equivalentdigital signal and provide the digital signal to circuitry 124. In someexamples, the digital processing circuit 124 processes, modifies,alters, or otherwise interacts with the data received from the ADC 122to create a signal that includes the data to provide to the interface112. For example, the digital processing circuit 124 may receive asignal at a sampling rate of the ADC 122 and may down convert the signalto reduce a frequency of the signal and/or perform decimation of data ofthe signal. In some implementations, the DSA 120, the ADC 122, and thedigital processing circuit 124 form, or are components of, a feedbacksignal path of the transceiver 102. The DSA 126 is coupled andconfigured to receive data from the amplifier 110 and provide data tothe ADC 128. The ADC 128 is coupled and configured to provide data tothe circuit 130. In some examples, the circuit 130 processes, modifies,alters, or otherwise interacts with the data received from the ADC 128to create data signal to provide to the interface 112. In someimplementations, the DSA 126, the ADC 128, and the circuit 130 form, orare components of, a receive signal path of the transceiver 102. In someexamples, the Fref generation circuit 132 provides Fref to the PLLcircuit 134. Based on Fref, the PLL provides a clock signal to the DAC116, the ADC 122, and the ADC 128 to facilitate operation of the DAC116, the ADC 122, and the ADC 128, respectively.

As described above, in some operational circumstances harmonic couplingmay occur between or among components of the transceiver 102, such asbetween the DSA 118 and the amplifier 104. In other examples, theharmonic coupling is injected into a transmission signal chain of thetransceiver 102 at any location(s) within the transmission signal chainand not between any two specific components. This harmonic coupling mayinclude electro-magnetic coupling, substrate coupling, or a combinationthereof. In some examples, the harmonic coupling results from generationof Fref by the Fref generation circuit 132. This harmonic coupling canadversely affect transmissions by the transceiver 102, such that datatransmitted by the transceiver 102 may be unreliable at least partiallyresulting from the harmonic coupling. The coupling may also causeemissions of the transceiver 102 to exceed regulatory specifications forthe transceiver 102, such as regulatory specifications regarding a levelof spurious emissions outside of a frequency band of transmission by thetransceiver 102. To compensate for, correct for, or otherwise mitigatethe effects of the harmonic coupling, the circuit 114 may combine acontrolled frequency spur with data received from the interface 112prior to providing the data to the DAC 116. The frequency spur may becontrolled such that it has a programmed amplitude, frequency, and/orphase based on determinations, calculations, estimations, or otherprocessing performed by the transceiver 102. In some examples, at leastsome of the processing is performed during a calibration operation ofthe transceiver 102, such as during a power-up phase of the transceiver102. The processing may further track or monitor signals associated withthe transceiver 102 subsequent to the power-up phase (e.g., during anoperational phase) to address transient, temperature, or othervariations that may occur. Some of these variations may include changesto the amplitude or phase based on time or temperature variations. Theprocessing may include estimation based on data received via thefeedback signal path such that the frequency spur may be based on,derived from, or otherwise related to data received by the transceiver102 via the feedback signal path.

FIG. 2 is a block diagram of a transceiver 102, in accordance withvarious examples. As shown in FIG. 2 , in some examples the circuit 114includes an adder 202 and a digital up-conversion (DUC) circuit 204.Although shown in FIG. 2 as a single component, in various examples theDUC circuit 204 may include multiple stages to provide signal processingfunctionality, such as interpolation filters, mixers, etc. Adder 202(and other adders illustrated in the drawings) may be implemented usingconventional circuitry or may be implemented by connecting conductors,each carrying separate signals, so that the connection results in thesum their signals at or near the point of connection. In some examples,the digital processing circuit 124 includes a mixer 206, a digitaldecimation chain (DDC) 208, and an estimation circuit 210. In anexample, the DUC 204 may include, for example, a processor, a statemachine, logic circuitry, digital circuitry, memory, analog circuitry,software and/or any combination thereof suitable for performing datainterpolation, frequency conversion (e.g., such as up conversion), andthe like. The mixer 206 may include, for example, a processor, a statemachine, logic circuitry, digital circuitry, memory, analog circuitry,software and/or any combination thereof suitable for performing signalmixing. In an example, the mixer 206 includes a numerically controlledoscillator (NCO) to generate or otherwise provide a local oscillatorsignal at a programmed frequency. The DDC 208 may include, for example,a processor, a state machine, logic circuitry, digital circuitry,memory, analog circuitry, software and/or any combination thereofsuitable for performing signal decimation. The DDC 208 may include, forexample, a processor, a state machine, logic circuitry, digitalcircuitry, memory, analog circuitry, software and/or any combinationthereof suitable for performing the functions described herein.

In some examples, the adder 202 receives data from the interface 112 andadds a signal which corresponds to a digital representation of acontinuous wave tone of frequency f_(spur) to the received data to formcompensated data. In some embodiments, the added frequency spur maycorrect for or mitigate the effects of the undesired harmonic coupling.The amplitude, frequency and/or phase of the added frequency spur may bedetermined during power-up calibration and/or during run-time (missionmode), to address time-related (aging) and/or temperature variations(for example). The compensated data is provided to the DUC circuit 204for conversion prior to providing to the DAC 116. The DUC circuit 204scales (e.g., up converts) a sample rate of the compensated data, suchas from a baseband frequency (or baseband frequency as modified byf_(spur)) to an intermediate frequency or a transmission frequency ofthe transceiver 102. The mixer 206 receives a digital version of theoutput of power amplifier 104 via DSA 120 and ADC 122. Mixer 206 mixesthe digital signal output by ADC 122 and provides the mixed version tothe DDC 208 and the estimation circuit 210. For example, the mixer 206may convert the output of the ADC 122 from a radio frequency signal to abaseband or other frequency signal, such as by performing frequencytranslation. The DDC 208 modifies a sample rate of the output of themixer 206, such as from an ADC sampling frequency to an interface rateof the interface 112 or another component (not shown) to which the DDC208 is coupled. The DDC 208 provides the modified sampling rate data asan output, such as for providing to the interface 112.

The estimation circuit 210 estimates a value of the harmonic coupling,during an initial calibration of the device or during run-mode asdescribed above. For example, a signal (e.g., a digital signal, such asdata) may be provided to the adder 202 to cause a continuous wave toneat a programmed baseband frequency (f_(B1)) to be transmitted by thetransmit signal path. The signal may be provided by a Fref canceller212. The Fref canceller 212 may include, for example, a processor, astate machine, logic circuitry, digital circuitry, memory, analogcircuitry, software and/or any combination thereof. The Fref canceller212 may be configured to provide a signal at a programmed amplitude,frequency, and phase (or provides a digital signal that, when convertedto an analog signal, has a programmed amplitude, frequency and phase).For example, the Fref canceller 212 may provide a digital representationof a continuous wave tone, as described herein, at frequency f_(spur).In some examples, f_(B1) is selected such that a frequency(f_(transmit)) of a signal at an output of the amplifier 104 isapproximately equal to

f _(transmit)=LO+f _(B1),  (1)

which is approximately equal to a frequency of the harmonic coupling,and in which LO is a local oscillator carrier frequency of the transmitsignal path. The estimation circuit 210 may estimate the value of theharmonic coupling according to any suitable process. In an example, theestimation circuit 210 may measure an amplitude and phase of a directcurrent (DC) signal provided as an output of the mixer 206. Themeasurement may be performed, for example, via an infinite impulseresponse (IIR) filter based on an output of a mixer that has a localoscillator tuned to a frequency of LO+f_(B1). In another example, themixer 206 has an offset from f_(B1) and the estimation circuit 210determines the amplitude and phase of the resulting signal, such as viaa fast Fourier transform (FFT) or Goertzel processing, to determine theamplitude and phase of f_(B1).

The following description refers to particular frequencies to aid inclarity and understanding of this disclosure. However, such frequenciesare exemplary and shall not be construed as limiting the examples ofthis disclosure to only the example frequencies recited. Assuming thatthe signal at frequency LO+f_(B1) is provided by the transmit signalchain (e.g., provided by the amplifier 104), a signal provided at theoutput of the ADC 122 is located at frequency f_(FB,LO). For example, ifLO is 3500 megahertz (MHz) and f_(B1) is 10 MHz, then a frequency at theoutput of the amplifier 104 is 3510 MHz. For a sampling frequency of theADC 122 of 3000 megasamples per second (MSPS), after sampling by the ADC122, the 3510 MHz signal will be at 510 MHz due to aliasing. Thus, inthis example, f_(FB,LO) is 510 MHz.

In an example, the mixer 206 mixes an output signal of the ADC 122 witha local oscillator signal corresponding to f_(FB,LO) to cause the mixer206 to down convert the continuous wave tone to DC, as represented by acomplex signal. This complex signal may be measured by an IIR, such asimplemented in the estimation circuit 210, to determine the amplitudeand phase of the DC representation of the continuous wave tone. Forexample, the IIR measures signal levels in the real and imaginary partsof the complex signal. Assuming the DC estimation in the real andimaginary parts of the signal is DCest₁ and DCest_(Q), and togetherprovide measurements m₁ and m₂, respectively, which will be describedbelow with respect to performing the calibration. In at least someexamples, m₁ and m₂ are complex values having both in-phase (I) and aquadrature phase (Q) components.

A local oscillator signal having a frequency of 500 MHz, when mixed withthe output signal of the ADC 122, may cause an output of the mixer 206to be the continuous wave tone at a frequency of f_(B1). In an example,to determine the amplitude and phase of the real and imaginary parts ofthe continuous wave tone, the estimation circuit 210 may perform a FFTon an output of the DDC 208. In another example, to determine theamplitude and phase of the continuous wave tone, the estimation circuit210 may perform a FFT on an output of the mixer 206. In variousexamples, for an interface rate (e.g., the clocking rate of interfacecircuitry 112) of 245.76 MSPS, a 512-point FFT provides a frequencyresolution of 0.48 MHz. To facilitate accurate amplitude and phasemeasurement, the frequency at the output of the DDC 208 (f_(FB,B1))should correspond to a particular frequency bin (f_(bin)) and notbetween frequency bins, which may cause inaccuracy in measurements. Inthe above example, because the resolution of the FFT is 0.48 MHz, f_(B1)is chosen as 9.6 MHz so that

$f_{bin} = {\frac{9.6}{0.48} = {2{0.}}}$

The measurement of the real and imaginary components of f_(bin),including amplitude and phase information of the tone on f_(bin),provide m₁ and m₂, which will be described below with respect toperforming the calibration.

A signal from the transmit signal path to the feedback signal pathpasses through a channel (e.g., a medium through which a signal passesfrom the output of the amplifier 104 to the input of the DSA 120). Thesignals are complex baseband signals represented with amplitude andphase information. The harmonic coupling spur has an amplitude (α) and aphase (ϕ), and h is the coefficient for the channel (e.g., an amplitudeand phase response of the channel). The continuous wave tone has afrequency f_(B1), as described above, and an amplitude A₁. The basebandmodel of the signal at the feedback signal path output (e.g., an outputof the mixer 206 or of the digital processing circuit 124) isrepresented by

h(A ₁ +αe ^(−jϕ))=m ₁  (2)

Two measurements may be performed at the output of the feedback signalpath with known amplitudes A₁ and A₂ for the continuous wave toneprovided by the Fref canceller 212 such that

h(A ₂ +αe ^(−jϕ))=m ₂  (3)

For example, taking A₁=A and A₂=−A, then

$\begin{matrix}{{h = \frac{m_{1} - m_{2}}{2A}};} & (4)\end{matrix}$ and $\begin{matrix}{{\alpha e^{{- j}\phi}} = {\frac{m_{1} + m_{2}}{2h}.}} & (5)\end{matrix}$

Thus, the magnitude and phase of

$\frac{m_{1} + m_{2}}{2h}$

provides an estimate for α and phase phase₁=−ϕ. The amplitude and phaseof the continuous wave tone at frequency f_(spur) to mitigate theharmonic coupling is determined as α and π+phase₁, respectively. In someexamples, this amplitude and phase is useful for the estimation circuit210 to provide the continuous wave tone at frequency f_(spur) tomitigate the harmonic coupling. In other examples, the amplitude andphase is provided by the estimation circuit 210 to another component(not shown) to cause or otherwise aid the other component in providingthe continuous wave tone at frequency f_(spur) to mitigate the harmoniccoupling. In other examples, the estimation circuit 210 provides thereal and imaginary, or in-phase and quadrature, parts of the continuouswave tone at frequency f_(spur) to mitigate the harmonic coupling. Insome examples, that other component may be the Fref canceller 212.

In this disclosure it is assumed that the carrier frequency of atransmit channel imparting the harmonic coupling and a transmit channelbeing affected by the harmonic coupling is the same. Also, thetransceiver 102 may perform pre-compensation for f_(B1) based ondeterminations made during power-up of the transceiver 102 and performcompensation at a later time after power-up according to another carrierfrequency.

While the harmonic coupling is generally described herein as occurringbetween the DSA 118 and the amplifier 104 (e.g., post-DSA coupling), insome examples the harmonic coupling alternatively, or additionally,occurs between the DAC 116 and the DSA 118 (e.g., pre-DSA coupling).Coupling coefficients of the harmonic coupling may be denoted as α_(pre)and α_(post) for pre-DSA coupling and post-DSA coupling, respectively.Thus, spur correction coefficients corresponding to α_(pre) and α_(post)in the digital domain are α_(pre,corr)e^(−jφ) and α_(post,corr)e^(−jφ).In an example, the power-up calibration may be performed for multipleattenuation settings of the DSA 118. Based on a current attenuationsetting of the DSA 118, spur correction coefficients may be determinedand the continuous wave tone at frequency f_(spur) be applied to thetransceiver 102. In another example, the coupling coefficient α, asdescribed above, can be separated into α_(pre) and α_(post) for thetransmit signal path. The components α_(pre) and α_(post) are estimatedby performing the calibration measurement at two selected gain steps ofthe transmit signal path. Assuming the gain settings are g₁ and g₂, thenthe measured coupling at these two gain settings are

α_(pre) *g ₁+α_(post)=α₁ and  (6)

α_(pre) *g ₂+α_(post)=α₂.  (7)

Because g₁ and g₂ are selected, or programmed values, α_(pre) andα_(post) can be determined. For example, if the gain transmit signalpath for the kth gain index is g_(ak), then the post-DSA couplingcomponent is multiplied by 1/g_(ak). Pre and post digital correctionfactors to be used for the kth gain setting of transmit signal pathchain are updated as

α_(pre, corr)e^(−jφ) and$\frac{\alpha_{{post},{corr}}}{g_{ak}}{e^{{- j}\phi}.}$

In another example, the spur correction for multiple attenuationsettings of the DSA 118 in the transmit signal path is determined andstored for use in mitigation of harmonic coupling, such as by storingthe correction values in a lookup table.

FIG. 3 is a block diagram of a transceiver, in accordance with variousexamples. In some examples, the DUC circuit 204 implements up conversionin multiple stages. A two-stage up conversion is shown in FIG. 3 , butany number of stages may be useful. For example, the DUC circuit 204includes a circuit 302, a mixer 304, a circuit 306, a mixer 308, and acircuit 310. The mixer 304 and the mixer 308 may each have the same ordifferent resolutions and may each respectively perform frequencytranslation to increase a frequency of a received signal prior tooutput. In some examples, the mixer 304 and the mixer 308 are eachimplemented as multipliers. The circuits 302, 306, 310 may be of anysuitable architecture to manipulate a received signal to provide amodified signal, the scope of which is not limited herein. For example,the circuits 302, 306, 310 may include analog and/or digital circuitrycomponents. In at least some examples, the circuits 302, 306, 310 arecomponents of a multi-stage DUC, such that the circuits 302, 306, 310are, or include circuitry of, digital or analog filter circuits. Each ofthe circuits 302, 306, and 310 may have associated delays based on theirarchitectures. For example, FIG. 3 assumes delays represented as τ₁, τ₂and τ₃ between the adder 202 and the mixer 304, between the mixer 304and the mixer 308, and between the mixer 308 and a point in the transmitsignal path at which the harmonic coupling occurs, respectively.

Assuming f_(B1) is the baseband frequency of the continuous wave tone atfrequency f_(spur), it is up converted by the mixer 304 and the mixer308 to cancel the harmonic coupling at frequency f_(harm). Assuming, forexample, the frequency of the mixer 304 (e.g., 1^(st) stage mixer) is f₁and mixer 308 (e.g., 2^(nd) stage mixer) is f₂, in a first measurement,the phase of f_(B1) is θ₁ to mitigate the harmonic coupling. Thebaseband model for the transceiver 102 provides

θ₁−2πf _(B1)τ₁=ϕ_(harm)+π,  (8)

where ϕ_(harm) is the phase of the harmonic coupling. Assuming themixing frequency of the mixer 304 is modified to f₁+Δ₁ and mixer 308 iskept at f₂, the baseband frequency of the continuous wave tone atfrequency f_(spur) is modified to f_(B1)−Δ₁ to mitigate the harmoniccoupling. Let the phase of the baseband tone to mitigate the harmoniccoupling be θ₂. The power-up calibration described above with respect toFIG. 2 . is repeated for this new frequency to determine the phase.Because

θ₂−2π(f _(B1)−Δ₁)τ₁=ϕ_(harm)+π,  (9)

then

2πΔ₁τ₁=θ₁−θ₂.  (10)

Thus, the phase change due to Δ₁ frequency change in mixer 304 isdetermined according to the above relation. In at least some examplesthe frequency change in mixer 304 is an integer multiple of Δ₁. Thephase change due to the mixer frequency change is determined bymultiplying the phase change due to Δ₁. For example, if the mixer 304frequency is shifted to f₁+k₁Δ₁ then the phase of the continuous wavetone at frequency f_(spur) to mitigate the harmonic coupling isθ₁+k₁(θ₂−θ₁).

Similarly, the step change of the mixer 308 may be considered.Considering the baseband model with carrier frequency being that ofmixer 308, the phase θ₁ to mitigate the harmonic coupling can also bedescribed as

θ₁−2πf _(B1)τ₁−2π(f _(B1) +f ₁)τ₂=ϕ_(harm)+π,  (11)

where f_(B1) is the frequency of the spur being injected by Frefcanceller 212 to the adder 202 and f₁ is the local oscillator frequencyof the mixer 304. Assume the mixer 308 frequency is shifted to f₂+Δ₂.The power-up calibration described above with respect to FIG. 2 may berepeated for the new frequency of the mixer 308 to determine a newphase, θ₃. For example, phase θ₃ may be used to mitigate f_(harm), so

θ₃−2π(f _(B1)−Δ₂)τ₁−2π(f _(B1) +f ₁−Δ₂)τ₂=ϕ_(harm)+π.  (12)

To maintain the compensation for the harmonic coupling, the basebandfrequency of the continuous wave tone at frequency f_(spur) for therepeated power-up calibration may be changed to f_(B1)−Δ₂. From theabove two relations, it can be determined that

$\begin{matrix}{{{2\pi\Delta_{2}\tau_{2}} = {{\theta_{3} - \theta_{1} - {2\pi\Delta_{2}\tau_{1}}} = {\theta_{1} - \theta_{3} - {\frac{\Delta_{2}}{\Delta_{1}}\left( {\theta_{1} - \theta_{2}} \right)}}}}.} & (13)\end{matrix}$

In at least some examples, the frequency change in mixer 308 is chosenas an integer multiple of Δ₂. For example, if the mixer 308 frequency isshifted to f₂+k₂Δ₂, then the phase of the continuous wave tone atfrequency f_(spur) to mitigate the harmonic coupling is θ₁+k₂(θ₃−θ₁). Inat least some examples, if frequencies of both the mixer 304 and mixer308 are changed according to f₁+k₄Δ₁ and f₂+k₃Δ₂, respectively, thephase of the continuous wave tone at frequency f_(spur) to mitigate theharmonic coupling is θ₁+k₄(θ₂−θ₁)+k₃(θ₃−θ₁).

Because the pre-compensation is to mitigate the harmonic coupling in theanalog domain, the magnitude of the harmonic coupling to be correctedmay not depend on the carrier frequency of the transmit signal path.However, the phase of the continuous wave tone at frequency f_(spur) maydepend on the carrier frequency of the transmit signal path.

During power-up calibration, as described above, the amplitude and phaseof the continuous wave tone at frequency f_(spur) in the baseband isdetermined. In addition to the above calibration steps, calibration maybe performed with multiple shifts of the local oscillator frequencies ofboth the mixer 304 and mixer 308. For example, calibration may beperformed with a unit step change in the carrier frequency. In anexample, if the step change for the carrier frequency is 1 kilohertz(kHz) and the phase change of the continuous wave tone at frequencyf_(spur) for 1 kHz change in carrier frequency is ϕ_(1 KHz) then for acarrier frequency change by a multiple m of 1 kHz, the phase change inthe continuous wave tone at frequency f_(spur) for the new carrierfrequency=m*ϕ_(1 KHz). In another example, the phase change is measuredfor multiple steps of the carrier frequency. For example, phase changeis measured for a shift of 1 kHz, 10 kHz, 100 kHz, and so on. Themeasured phase change is represented as ϕ_(1 KHz), ϕ_(10 KHz),ϕ_(100 KHz) and so on, respectively. In the system, the change incarrier frequency is expressed as multiples of steps of 1 kHz, 10 kHz,100 kHz and so on. The multiples m_(1 kHz), m_(10 kHz), m_(100 kHz) andso on, respectively describe the change in the carrier frequency. Thephase change for the continuous wave tone at frequency f_(spur) for thenew carrier frequency may then be computed asϕ_(LO change)=m_(1 kHz)ϕ_(1 kHz)+m_(10 kHz)ϕ_(10 kHz)+m_(100 kHz)ϕ_(100 kHz). . . .

FIG. 4 is a flow diagram of a method 400 of operation of a transceiver,in accordance with various examples. In at least some examples, thetransceiver is the transceiver 102. Accordingly, reference may be madeto components or signals of the transceiver 102, as described above withreference to other figures herein. In some examples, the transceiver isoperated to perform estimation and/or pre-compensation of harmoniccoupling. For example, left uncompensated, the harmonic coupling mayaffect a signal being transmitted by the transceiver 102, adverselyaffecting a component, device, or system that receives and operatesaccording to that signal.

At operation 405, a value of harmonic coupling is determined. In someexamples, the value of the harmonic coupling is represented as anamplitude and a phase of the harmonic coupling. In other examples, thevalue of the harmonic coupling is represented as the real and imaginary(or in-phase and quadrature) components of the harmonic coupling. Thevalue of the harmonic coupling may be determined as described aboveherein, such as during a calibration phase of operation (e.g., atstart-up and/or during mission mode operation at certain times and/orintervals of time). For example, calibration data may be transmitted bythe transceiver and feedback data derived from the transmitted data maybe processed to determine the value of the harmonic coupling. In someexamples, the value of harmonic coupling is determined for multipletransmission center frequencies, such as by stepping through range oftransmission center frequencies.

At operation 410, pre-compensation for the harmonic coupling isperformed. For example, based on the determined amplitude and phase ofthe harmonic coupling, the transceiver determines and provides acontinuous wave tone at frequency f_(spur), as described above herein.The transceiver may add the continuous wave tone to data received by thetransceiver for transmission to form compensated data. The compensateddata may no longer be representative of values that were represented bythe data prior to the addition of the continuous wave tone and formationof the compensated data. However, the compensated data, after beingaffected by the harmonic coupling described herein, based on theperformed pre-compensation, may again be representative of values thatwere represented by the data prior to the addition of the continuouswave tone and formation of the compensated data. This is in contrast tothe data, left uncompensated, being affected by the harmonic couplingsuch that, after being affected by the harmonic coupling describedherein, the data may no longer be representative of values that wererepresented by the data prior to the effects of the harmonic coupling.

In an example embodiment, the amplitude and phase of spurious harmoniccoupling signal(s) may be calculated/quantified during a power-upcalibration of the transceiver system, and such spurious signal may bemitigated/compensated for by injecting a transmit spur (e.g., in thedigital baseband) during run-time/mission mode operation. These valuesmay be used during run-time/mission mode operation of the transceiversystem to mitigate/compensate for the harmonic coupling signal(s). Insome embodiments, additional background tracking of the amplitude andphase of spurious harmonic coupling signal(s) may becalculated/quantified during run-time/mission mode operation. Thisadditional information can be used to compensate for/mitigate systemvariations due to aging and/or temperature. In some example embodiments,during power-up calibration, the output of digital processing circuit124 (FIG. 1 ) is measured where a known signal is provided at the outputof circuitry 114 (FIG. 1 ). The amplitude and phase of the harmoniccoupling signal(s) may be determined by altering the signal output bythe digital processing circuit 124. In some example embodiments,compensation for the spurious harmonic coupling signal(s) may beperformed in the digital baseband. In other example embodiments, thecompensation may be performed in the digital passband.

The term “couple” is used throughout the specification. The term maycover connections, communications, or signal paths that enable afunctional relationship consistent with this description. For example,if device A generates a signal to control device B to perform an action,in a first example device A is coupled to device B, or in a secondexample device A is coupled to device B through intervening component Cif intervening component C does not substantially alter the functionalrelationship between device A and device B such that device B iscontrolled by device A via the control signal generated by device A.

A device that is “configured to” perform a task or function may beconfigured (e.g., programmed and/or hardwired) at a time ofmanufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof. A circuitor device that is described herein as including certain components mayinstead be adapted to be coupled to those components to form thedescribed circuitry or device.

As used herein, the terms “terminal”, “node”, “interconnection”, “pin”,“ball” and “lead” are used interchangeably. Unless specifically statedto the contrary, these terms are generally used to mean aninterconnection between or a terminus of a device element, a circuitelement, an integrated circuit, a device or other electronics orsemiconductor component. While certain elements of the describedexamples are included in an integrated circuit and other elements areexternal to the integrated circuit, in other example embodiments,additional or fewer features may be incorporated into the integratedcircuit. In addition, some or all of the features illustrated as beingexternal to the integrated circuit may be included in the integratedcircuit and/or some features illustrated as being internal to theintegrated circuit may be incorporated outside of the integrated. Asused herein, the term “integrated circuit” means one or more circuitsthat are: (i) incorporated in/over a semiconductor substrate; (ii)incorporated in a single semiconductor package; (iii) incorporated intothe same module; and/or (iv) incorporated in/on the same printed circuitboard.

Unless otherwise stated, “about,” “approximately,” or “substantially”preceding a value means +/−10 percent of the stated value. Modificationsare possible in the described examples, and other examples are possiblewithin the scope of the claims.

What is claimed is:
 1. A circuit having an input operable to receivedata and an output operable to provide a transmitted signal, the circuitcomprising: a transmission signal chain including: a harmonic couplingcancellation circuit operable to output a harmonic coupling cancellationsignal; a digital up-conversion (DUC) circuit having an output, a firstinput operable to receive the harmonic coupling cancellation signal, anda second input coupled to the circuit input, the DUC circuit operable tomodify the data by the harmonic coupling cancellation signal; and adigital-to-analog converter (DAC) having an input coupled to the outputof the DUC and having an output, the DAC configured to provide thetransmitted signal at the output of the DAC; and a feedback signal chainincluding an estimation circuit, the estimation circuit operable to:estimate a spurious harmonic coupling signal according to thetransmitted signal; and provide values representative of the estimate ofthe spurious harmonic coupling signal to the harmonic couplingcancellation circuit, wherein the harmonic coupling cancellation signalis based on the estimate of the spurious harmonic coupling signal. 2.The circuit of claim 1, wherein the transmitted signal includesharmonics of a reference clock of the circuit, and wherein the spuriousharmonic coupling signal is representative of the harmonics of thereference clock.
 3. The circuit of claim 1, wherein the valuesrepresentative of the estimate are provided as amplitude and phasevalues.
 4. The circuit of claim 3, wherein the amplitude and phasevalues are provided for multiple transmission center frequencies of thecircuit for the transmitted signal.
 5. The circuit of claim 1, whereinthe circuit includes multiple transmit signal chains and the valuesrepresentative of the estimate of the spurious harmonic coupling signalare determined for each of the multiple transmit signal chains.
 6. Thecircuit of claim 1, wherein the harmonic coupling cancellation circuitis operable to provide a signal having programmed values during acalibration mode of operation of the circuit to enable estimating thespurious harmonic coupling signal based on the programmed values.
 7. Thecircuit of claim 1, wherein the harmonic coupling cancellation circuitis operable to provide a signal having the values representative of theestimate of the spurious harmonic coupling signal during a operationalmode of operation of the circuit to perform pre-compensation of thetransmitted signal according to the estimated spurious harmonic couplingsignal.
 8. The circuit of claim 1, wherein the circuit is programmableto transmit at one of multiple transmission center frequencies, andwherein the estimate of the spurious harmonic coupling signal isperformed for each of the multiple transmission center frequencies.
 9. Asystem, comprising: an amplifier having an input and an output; and atransceiver having: a communication interface; a transmit signal chainhaving an input coupled to an output of the communication interface andan output coupled to the input of the amplifier, wherein the transmitsignal path is configured to provide a signal for transmission to theamplifier; and a feedback signal chain having an input coupled to theoutput of the amplifier and an output coupled to an input of thecommunication interface, wherein the feedback signal chain is configuredto: estimate a spurious harmonic coupling component of a signaltransmitted by the amplifier; and provide values representative of theestimate of the spurious harmonic coupling component to the transmitsignal path for compensation for the spurious harmonic couplingcomponent in the signal for transmission.
 10. The system of claim 9,wherein the transmit signal path includes a cancellation circuitconfigured to perform the compensation for the spurious harmoniccoupling component during an operational mode of operation of thesystem.
 11. The system of claim 10, wherein, during a calibration modeof operation of the transceiver, the cancellation circuit is configuredto provide a signal having a programmed value to the transmit signalpath for forming the signal for transmission, the signal having theprogrammed value to facilitate the feedback signal chain estimating ofthe spurious harmonic coupling component.
 12. The system of claim 9,wherein the transceiver is programmable to transmit at one of multipletransmission center frequencies.
 13. The system of claim 12, wherein,during a calibration mode of operation of the transceiver and for eachtransmission center frequency of the multiple transmission centerfrequencies, the cancellation circuit is configured to provide a signalhaving a programmed value to the transmit signal path for forming thesignal for transmission, the signal having the programmed value tofacilitate the feedback signal chain estimating of the spurious harmoniccoupling component for the transmission center frequency of the multipletransmission center frequencies.
 14. The system of claim 9, wherein theinterface is a serializer/deserializer (SerDes) interface or a JESDinterface.
 15. The system of claim 9, wherein the values representativeof the estimate of the spurious harmonic coupling component are in-phaseand quadrature component values of the spurious harmonic couplingcomponent.
 16. A method, comprising: determining, via a circuit, anestimated value of harmonic coupling in a transmitted signal via afeedback signal path that receives the transmitted signal; andperforming pre-compensation for the harmonic coupling based on theestimated value, the pre-compensation performed in the circuit.
 17. Themethod of claim 16, wherein the estimated value of the harmonic couplingis determined for each transmission center frequency of multipleprogrammable transmission center frequencies of the circuit.
 18. Themethod of claim 16, wherein the estimated value of the harmonic couplingis represented as an amplitude and a phase of the harmonic coupling. 19.The method of claim 18, wherein the estimated value of the harmoniccoupling is determined during a calibration mode of operation of thecircuit and the amplitude and phase are monitored during an operationalmode of operation of the circuit for variance resulting from time ortemperature.
 20. The method of claim 16, wherein the pre-compensation isperformed in one of digital baseband or digital passband of the circuit.